ANS: A A. Correct response: The usual treatment of methemoglobinemia is infusion of methylene blue, which increases NADH methemoglobin reductase. Methemoglobinemia can also be treated with ascorbic acid (vitamin C). The production of methemoglobin in patients treated with iNO is dose-dependent; methemoglobinemia is rare at usual therapeutic doses of less than 20 ppm.B. Incorrect response: See explanation A.C. Incorrect response: See explanation A.D. Incorrect response: See explanation A.